Inorganic membrane for extracting helium as well as preparation method and application of inorganic membrane

Abstract

The invention provides an inorganic membrane for extracting helium as well as a preparation method and application of the inorganic membrane. The inorganic membrane comprises a molecular sieve membrane and a protective coating, the molecular sieve membrane comprises a carrier and a molecular sieve layer, the protective coating is located on the surface of the side, away from the carrier, of the molecular sieve layer, and the protective coating comprises beta-cyclodextrin and / or polydimethylsiloxane. The inorganic membrane for helium extraction comprises the molecular sieve membrane and the protective coating, the protective coating comprises beta-cyclodextrin and / or polydimethylsiloxane, and due to the existence of the protective coating, the separation selectivity of the inorganic membrane on helium in mixed gas containing helium and methane can be high.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, and particularly relates to an inorganic membrane for helium extraction, its preparation method, and its application. Background Technology

[0002] Helium is a colorless, odorless, gaseous, inert gas at room temperature. It is one of the most difficult-to-liquefy inert gases and is widely used in aerospace, petrochemicals, nuclear industry, laser technology, medicine, scientific research, and low-temperature superconductivity. Cryogenic distillation is a relatively mature method for extracting helium from natural gas, holding over 90% of the market share. However, cryogenic distillation requires large investments and consumes a lot of energy, making it less economically viable for extracting helium from lean natural gas. Membrane separation technology can achieve efficient separation of helium from other gas molecules without a phase change, and holds promise for engineering applications in extracting helium from lean natural gas.

[0003] Invention application CN115414793A discloses an STT molecular sieve membrane suitable for helium purification and its preparation method. A nano-SiO2 particle transition layer is constructed between the support and the STT molecular sieve layer. STT is well-suited for helium purification. However, the hollow fiber support and the molecular sieve membrane have significantly different coefficients of thermal expansion. During hydrothermal synthesis and high-temperature calcination, intergranular defects are easily generated in the membrane layer, reducing the molecular sieve membrane's selectivity for separating helium from a mixture of helium and methane.

[0004] Invention application CN101874990A discloses a method for repairing intercrystalline pores in molecular sieve membranes, which uses silane hydrolysis to deposit silicon dioxide to repair intercrystalline pore defects. However, the method is only effective for eliminating intercrystalline defects with a diameter greater than 4 nm. Since the kinetic diameters of gas molecules involved in helium extraction from natural gas are all less than 0.5 nm, this method has limited effectiveness in improving the separation of helium from a mixture of helium and methane using STT molecular sieve membranes.

[0005] In summary, existing STT molecular sieve membranes exhibit poor selectivity for separating helium in mixed gases containing helium and methane (such as natural gas containing helium). Therefore, developing an inorganic membrane with high selectivity for separating helium in mixed gases containing helium and methane is a pressing technical problem that needs to be solved at this stage. Summary of the Invention

[0006] The main objective of this invention is to provide an inorganic membrane for helium extraction, which can improve the separation selectivity of helium in a mixture of helium and methane.

[0007] The present invention also provides a method for preparing an inorganic membrane, which can prepare the above-mentioned inorganic membrane, and the process is simple and low in cost.

[0008] The present invention also provides a method for helium extraction, which uses the above-mentioned inorganic membrane to adsorb helium in a mixed gas containing helium and methane, thereby improving the separation selectivity of helium in a mixed gas containing helium and methane.

[0009] In a first aspect, the present invention provides an inorganic membrane for helium extraction, comprising a molecular sieve membrane and a protective coating; the molecular sieve membrane comprises a carrier and a molecular sieve layer, the protective coating being located on the surface of the molecular sieve layer opposite to the carrier, and the protective coating comprising β-cyclodextrin and / or polydimethylsiloxane.

[0010] The inorganic membrane described above includes an STT molecular sieve layer.

[0011] The thickness of the protective coating in the inorganic film described above is 0.5-3 μm.

[0012] The inorganic membrane described above has a carrier thickness of 0.5-1.5 mm; and / or, the molecular sieve layer has a thickness of 4-15 μm.

[0013] Secondly, the present invention provides a method for preparing the inorganic membrane as described above, comprising the following steps:

[0014] 1) The molecular sieve membrane is placed in the impregnation solution and subjected to a first impregnation and lifting treatment and a second impregnation and lifting treatment in sequence to obtain an impregnated molecular sieve membrane; the impregnation solution includes functional components, the functional components including β-cyclodextrin and / or polydimethylsiloxane;

[0015] 2) The impregnated molecular sieve membrane is subjected to a first drying treatment and a second drying treatment in sequence to obtain the inorganic membrane.

[0016] In the inorganic membrane preparation method described above, the first immersion and lifting treatment time is 3-40 s, and the first immersion and lifting treatment rate is 0.2-3 cm / s; and / or, the second immersion and lifting treatment time is 3-40 s, and the second immersion and lifting treatment rate is 0.2-3 cm / s; and / or, the first drying treatment temperature is 15-30℃, and the first drying treatment time is 1-4 h; and / or, the second drying treatment temperature is 25-200℃, and the second drying treatment time is 0.5-1 h.

[0017] In the method for preparing the inorganic membrane as described above, the functional component includes polydimethylsiloxane, and the concentration of polydimethylsiloxane is 6-20%.

[0018] The functional component includes β-cyclodextrin, and the concentration of β-cyclodextrin is 1-3%.

[0019] The inorganic membrane preparation method described above, wherein the functional component includes polydimethylsiloxane, and the impregnation solution further includes a curing agent and n-heptane; the mass ratio of polydimethylsiloxane, curing agent, and n-heptane is 1:0.1:(5-15);

[0020] The functional component includes β-cyclodextrin, and the impregnation solution further includes deionized water; the mass ratio of β-cyclodextrin to deionized water is (1-3):100.

[0021] Thirdly, the present invention provides a method for helium extraction, comprising the following steps: using an inorganic membrane to adsorb helium from a mixed gas containing helium and methane, wherein the inorganic membrane includes the inorganic membrane described above or an inorganic membrane prepared by the method described above.

[0022] In the helium extraction method described above, the adsorption pressure is 0.1-5.2 MPa.

[0023] The inorganic membrane for helium extraction provided by the present invention includes a molecular sieve membrane and a protective coating, wherein the protective coating includes β-cyclodextrin and / or polydimethylsiloxane. The presence of the protective coating enables the inorganic membrane to have high selectivity for separating helium in a mixed gas containing helium and methane. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram of the structure of an inorganic membrane for helium extraction provided by the present invention;

[0026] Figure 2 A schematic diagram of a process for adsorbing helium from a mixed gas containing helium and methane, provided by the present invention;

[0027] Figure 3 (a) is a SEM image of the STT molecular sieve membrane of Comparative Example 1 of the present invention.

[0028] Figure 3 (b) is another SEM image of the STT molecular sieve membrane of Comparative Example 1 of the present invention.

[0029] Figure 4 (a) is a SEM image of an inorganic membrane for helium extraction according to Embodiment 2 of the present invention;

[0030] Figure 4(b) is another SEM image of the inorganic membrane for helium extraction according to Embodiment 2 of the present invention;

[0031] Figure 5 (a) is a schematic diagram of the contact angle of the STT molecular sieve membrane of Comparative Example 1 of the present invention;

[0032] Figure 5 (b) is a schematic diagram of the contact angle of the inorganic membrane for helium extraction in Embodiment 1 of the present invention;

[0033] Figure 6 This is a stability diagram of the inorganic membrane for helium extraction in Embodiment 1 of the present invention for separating helium from a mixed gas containing helium and methane.

[0034] Figure 7 This is a graph showing the helium separation performance of the inorganic membrane used for helium extraction in Embodiment 6 of the present invention for a mixed gas containing helium and methane. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] In a first aspect, the present invention provides an inorganic membrane for helium extraction, such as... Figure 1 As shown, it includes a molecular sieve membrane and a protective coating; the molecular sieve membrane includes a carrier and a molecular sieve layer, the protective coating is located on the surface of the molecular sieve layer opposite to the carrier, and the protective coating includes β-cyclodextrin and / or polydimethylsiloxane (PDMS).

[0037] The inorganic membrane for helium extraction provided by this invention has a protective coating applied to the surface of a molecular sieve layer. This protective coating comprises β-cyclodextrin and / or polydimethylsiloxane. The presence of this protective coating enables the inorganic membrane to achieve high selectivity for separating helium from helium-poor natural gas. Specifically, this can be manifested in the ability to separate helium from... Figure 7 As can be seen, under a high pressure of 5.2 MPa, the helium separation selectivity is 166, the helium recovery rate can reach 55.2%, and the helium concentration factor can reach 92, increasing the helium concentration from 0.075% to 6.9%. The reasons for this are twofold: firstly, the protective coating eliminates defects between the molecular sieve crystals; secondly, the molecular sieve layer and the protective coating form a bridging structure, effectively hindering the permeation and diffusion of large molecules such as methane, thus improving the separation selectivity of helium relative to methane.

[0038] In addition, the protective coating of the present invention can make full use of the hydrophobic properties of polymer materials to avoid the accumulation of water vapor molecules in the molecular sieve channels, thereby improving the water vapor tolerance of inorganic membranes during storage and use, extending the service life of inorganic membranes, and making the storage and application processes of inorganic membranes simpler.

[0039] This invention does not limit the specific type of carrier, as long as it can achieve the loading of the molecular sieve layer. For example, the carrier may include hollow fiber, sheet carrier, tubular carrier, etc.

[0040] The beneficial effects of this invention are that the inorganic membrane used for helium extraction includes a molecular sieve membrane and a protective coating. The protective coating includes β-cyclodextrin and / or polydimethylsiloxane. The presence of the protective coating enables the inorganic membrane to have high selectivity for separating helium in a mixed gas containing helium and methane, and the hydrophobicity of the protective coating can extend the service life of the inorganic membrane, making the storage and application process of the inorganic membrane simpler.

[0041] In some embodiments of the present invention, the molecular sieve layer includes an STT molecular sieve, specifically an STT molecular sieve layer formed from an STT molecular sieve.

[0042] The inorganic membrane for helium extraction provided by this invention includes an STT molecular sieve as its molecular sieve layer. Because the STT molecular sieve has a unique pore structure, seven-membered and nine-membered ring mass transfer channels intersect each other. The seven-membered ring channels are distributed along the [-101] direction with a pore size of 0.24 nm × 0.35 nm; the nine-membered ring channels are parallel to the

[101] direction with a pore size of 0.37 nm × 0.53 nm. The pore size of this molecular sieve is between the helium kinetic diameter (0.26 nm) and the methane kinetic diameter (0.38 nm). Therefore, the STT molecular sieve is an ideal molecular sieve for separating helium and methane, and can improve the separation selectivity of helium in a helium-methane mixture.

[0043] The STT molecular sieve layer can be prepared according to conventional methods in the art. For example, it can be prepared by referring to the preparation method described in invention application CN115414793A, specifically the preparation method described in Example 1 of that invention application. Exemplarily, the preparation method of the STT molecular sieve layer may include the following steps:

[0044] 1) A mixture comprising nano-SiO2 particles, STT ball-milled seed crystals, and STT molecular sieves is mixed with water to obtain a seed crystal solution;

[0045] 2) The support is pretreated with alkali to obtain the pretreated support; the pretreated support is then impregnated, dried and calcined with a seed solution to obtain the first intermediate.

[0046] 3) The mixture comprising the first intermediate, SiO2, template agent, and water is subjected to hydrothermal crystallization treatment to obtain the second intermediate; the template agent may be N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH).

[0047] 4) Under an ozone atmosphere, the template agent of the second intermediate is removed to obtain the STT molecular sieve layer.

[0048] In some embodiments of the present invention, the thickness of the protective coating is 0.5-3 μm.

[0049] In some embodiments, the thickness of the carrier is 0.5-1.5 mm.

[0050] In some embodiments, the thickness of the molecular sieve layer is 4-15 μm.

[0051] For example, the thickness of the protective coating can be in the range of 0.5 μm, 1 μm, 1.7 μm, 2 μm, 2.4 μm, 3 μm, or any combination thereof. The thickness of the carrier can be in the range of 0.5 mm, 0.7 mm, 1 mm, 1.2 mm, 1.5 mm, or any combination thereof. The thickness of the molecular sieve layer can be in the range of 4 μm, 6 μm, 8 μm, 10 μm, 15 μm, or any combination thereof.

[0052] In this invention, the thickness of the protective coating is within the above-mentioned range, which can further eliminate crystal defects in the molecular sieve layer, effectively hinder the permeation and diffusion of macromolecules such as methane, and improve the separation selectivity of helium relative to methane, thereby increasing the helium recovery rate and helium concentration factor.

[0053] When the thickness of the carrier is within the above range, it can provide better support for the molecular sieve layer and the protective coating, ensuring that the inorganic membrane will not crack or deform during use, and improving the mechanical strength and stability of the inorganic membrane.

[0054] The thickness of the molecular sieve layer within the above range can further improve the separation selectivity of helium in a mixture of helium and methane, which helps to separate helium from the mixture of methane and helium.

[0055] Secondly, the present invention provides a method for preparing the inorganic membrane as described above, comprising the following steps:

[0056] 1) The molecular sieve membrane is placed in the impregnation solution and subjected to a first impregnation and lifting treatment and a second impregnation and lifting treatment in sequence to obtain an impregnated molecular sieve membrane; the impregnation solution includes functional components, the functional components including β-cyclodextrin and / or polydimethylsiloxane;

[0057] 2) The impregnated molecular sieve membrane is subjected to a first drying treatment and a second drying treatment in sequence to obtain the inorganic membrane; the temperature of the second drying treatment is higher than the temperature of the first drying treatment.

[0058] In step 1) of this invention, the carrier is first sealed and protected. For example, for a molecular sieve membrane on a hollow fiber carrier, polytetrafluoroethylene tape can be wrapped around both ends of the molecular sieve membrane for sealing. Then, a protective layer is applied. The molecular sieve membrane is held with tweezers and placed in the prepared impregnation solution for a first impregnation and lifting treatment, controlling the time and rate of the first impregnation and lifting treatment. The end held by the tweezers is designated as end A, and the other end as end B. After the molecular sieve membrane coated with the impregnation solution is inverted, it is vertically immersed in the impregnation solution again for a second impregnation and lifting treatment, i.e., end B is on top and end A is on the bottom. After two coatings, an impregnated molecular sieve membrane is obtained. Because the impregnation solution includes the functional components β-cyclodextrin and / or polydimethylsiloxane, after the two impregnation and lifting treatments, a layer of impregnation solution containing β-cyclodextrin and / or polydimethylsiloxane can be evenly coated on the surface of the molecular sieve layer.

[0059] In step 2), the impregnated molecular sieve membrane obtained above is subjected to a first drying treatment. Since the temperature of the first drying treatment is lower than that of the second drying treatment, most of the organic solvent on the surface of the impregnated molecular sieve membrane is removed. Then, a second drying treatment is performed to completely remove the solvent on the surface of the impregnated molecular sieve membrane, forming a polymer protective coating on the surface of the molecular sieve layer away from the carrier. Alternatively, after the solvent on the surface of the impregnated molecular sieve membrane is removed, the functional components undergo cross-linking, forming a polymer protective coating on the surface of the molecular sieve layer away from the carrier, thus obtaining an inorganic membrane.

[0060] The preparation method of the present invention can prepare the inorganic membrane of the first aspect mentioned above. The preparation method is simple. The protective coating on the surface of the molecular sieve membrane can make the inorganic membrane highly selective for separating helium in a mixed gas containing helium and methane. The hydrophobicity of the protective coating can extend the service life of the inorganic membrane, making the storage and application process of the inorganic membrane more convenient.

[0061] In some embodiments of the present invention, the time for the first immersion lifting treatment is 3-40 seconds, and the rate of the first immersion lifting treatment is 0.2-3 cm / s.

[0062] In some embodiments, the second immersion lifting treatment time is 3-40 seconds, and the second immersion lifting treatment rate is 0.2-3 cm / s.

[0063] In some embodiments, the temperature of the first drying treatment is 15-30°C, and the time of the first drying treatment is 1-4 hours.

[0064] In some embodiments, the temperature of the second drying treatment is 25-200°C, and the time of the second drying treatment is 0.5-1h.

[0065] For example, the time for the first immersion and lifting treatment can be a range of 3s, 4s, 6s, 8s, 10s, 20s, 30s, 40s, or any combination thereof. The rate of the first immersion and lifting treatment can be a range of 0.2cm / s, 0.5cm / s, 0.7cm / s, 1cm / s, 1.2cm / s, 1.4cm / s, 2cm / s, 3cm / s, or any combination thereof. The time for the second immersion and lifting treatment can be a range of 3s, 4s, 6s, 8s, 10s, 20s, 30s, 40s, or any combination thereof. The rate of the second immersion and lifting treatment can be a range of 0.2cm / s, 0.5cm / s, 0.7cm / s, 1cm / s, 1.2cm / s, 1.4cm / s, 2cm / s, 3cm / s, or any combination thereof. The temperature of the first drying treatment can be a range of 15°C, 17°C, 20°C, 25°C, 30°C, or any combination thereof. The first drying treatment time can be within the range of 1 hour, 2 hours, 2.5 hours, 3 hours, 4 hours, or any combination thereof. The second drying treatment temperature can be within the range of 25°C, 50°C, 70°C, 100°C, 120°C, 150°C, 170°C, 200°C, or any combination thereof. The second drying treatment time can be within the range of 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, or any combination thereof.

[0066] In this invention, the time and rate of the first and second immersion lifting treatments are within the above-mentioned range, which allows the impregnation liquid containing functional components to be fully and uniformly coated on the surface of the molecular sieve layer.

[0067] The temperature and time of the first drying process are within the above range, which can fully remove most of the organic solvent from the surface of the impregnated molecular sieve membrane, facilitating the formation of a polymer protective coating on the surface of the molecular sieve layer during the subsequent second drying process.

[0068] The temperature and time of the second drying process are within the above range, which can further remove the solvent from the surface of the impregnated molecular sieve membrane and form a polymer protective coating on the surface of the molecular sieve layer away from the carrier, so as to further improve the separation selectivity of the inorganic membrane for helium in the helium and methane mixture.

[0069] In some embodiments of the present invention, the functional component includes polydimethylsiloxane, wherein the concentration of polydimethylsiloxane is 6-20%; the functional component includes β-cyclodextrin, wherein the concentration of β-cyclodextrin is 1-3%.

[0070] For example, the concentration of polydimethylsiloxane can be in the range of 6%, 8%, 10%, 15%, 17%, 20%, or any combination thereof; the concentration of β-cyclodextrin can be 1%, 1.5%, 2%, 2.5%, or 3%.

[0071] In this invention, the concentration of the functional components is within the above-mentioned range, which allows the thickness of the polymer protective coating formed on the surface of the molecular sieve layer to be within a suitable range, further eliminating crystal defects in the molecular sieve layer, effectively hindering the permeation and diffusion of macromolecules such as methane, and improving the separation selectivity of helium relative to methane.

[0072] In some embodiments of the present invention, the functional component includes polydimethylsiloxane, and the impregnation liquid further includes a curing agent and n-heptane; the mass ratio of polydimethylsiloxane, curing agent and n-heptane is 1:0.1:(5-15); the functional component includes β-cyclodextrin, and the impregnation liquid further includes deionized water; the mass ratio of β-cyclodextrin and deionized water is (1-3):100.

[0073] For example, the mass ratio of polydimethylsiloxane, curing agent, and n-heptane can be 1:0.1:5, 1:0.1:6, 1:0.1:7, 1:0.1:8, 1:0.1:9, 1:0.1:10, 1:0.1:11, 1:0.1:12, 1:0.1:13, 1:0.1:14, 1:0.1:15, or any two of these; the mass ratio of β-cyclodextrin and deionized water can be 1:100, 1.5:100, 2:100, 2.5:100, 3:100, or any two of these.

[0074] In this invention, when the protective coating of the inorganic membrane is polydimethylsiloxane, the functional components in the impregnation solution include polydimethylsiloxane, as well as a curing agent and n-heptane, to cause the polydimethylsiloxane to undergo cross-linking polymerization, forming a polymer protective coating on the surface of the molecular sieve layer. When the mass ratio of polydimethylsiloxane, curing agent, and n-heptane is within the aforementioned range, the polydimethylsiloxane can form a stable cross-linked network structure during the curing process, improving the mechanical properties and durability of the polymer protective coating.

[0075] In this invention, when the protective coating of the inorganic membrane is β-cyclodextrin, the functional component in the impregnation solution includes β-cyclodextrin and also includes deionized water, so that the β-cyclodextrin forms a polymer protective coating on the surface of the molecular sieve layer. Maintaining the mass ratio of β-cyclodextrin to deionized water within the above-mentioned range can improve the mechanical properties and durability of the polymer protective coating.

[0076] Thirdly, the present invention provides a method for helium extraction, comprising the following steps: using an inorganic membrane to adsorb helium from a mixed gas containing helium and methane, wherein the inorganic membrane includes the inorganic membrane described above or an inorganic membrane prepared by the method described above.

[0077] like Figure 1 As shown, this invention enables a mixture of helium and methane, such as an equimolar helium-methane mixture or helium-lean natural gas, to pass through an inorganic membrane. On the permeate side of the inorganic membrane, a helium-rich component is obtained, and on the osmate side, a methane-rich component is obtained. The helium concentration factor in the helium-rich component can reach 75-92 times. In other words, the use of the inorganic membrane can improve the separation selectivity of helium in a mixture of helium and methane.

[0078] In some embodiments of the present invention, the adsorption pressure is 0.1-5.2 MPa.

[0079] For example, the adsorption pressure can be a range of 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5.2 MPa or any combination thereof.

[0080] In this invention, controlling the adsorption pressure within the aforementioned range during the adsorption process, i.e., controlling the pressure of the natural gas to be adsorbed and separated within the aforementioned range, can further improve the selectivity of the inorganic membrane for separating helium in a mixture of helium and methane. The pressure can be controlled by the back pressure valve of the testing device.

[0081] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0082] Example 1

[0083] The helium extraction method in this embodiment includes the following steps:

[0084] 1) Preparation of PDMS solution: Weigh 49g of Sylgard 184 PDMS (Dow Corning), 4.9g of Sylgard 184 curing agent, and 246.1g of n-heptane to prepare a PDMS impregnation solution with a mass ratio of PDMS, curing agent, and n-heptane of 1:0.1:5, and a PDMS concentration of 16.3%. Place the prepared impregnation solution in a 500mL reagent bottle and stir vigorously at 700rpm for 12 hours.

[0085] 2) Preparation of STT molecular sieve membrane: STT molecular sieve membrane was prepared according to the preparation method described in Example 1 of invention application CN115414793A.

[0086] 3) Coating with a PDMS protective layer: Wrap the two ends of the STT molecular sieve membrane with PTFE tape, hold the STT molecular sieve membrane with tweezers, and place it in the PDMS impregnation solution prepared in step 1). Control the first impregnation and lifting time to 40s and the first impregnation and lifting rate to 0.2cm / s. At this time, the end held by the tweezers is recorded as end A, and the other end as end B. After inverting the STT molecular sieve membrane coated with PDMS impregnation solution, it is vertically impregnated again in the PDMS impregnation solution prepared in step 1), i.e., end B on top and end A on the bottom. Control the second impregnation and lifting time to 40s and the second impregnation and lifting rate to 0.2cm / s to obtain an impregnated molecular sieve membrane. The impregnated molecular sieve membrane is subjected to a first drying treatment at 25℃ for 1h, and then placed in an oven for a second drying treatment at 100℃ for 1h, with a heating and cooling rate of 1℃ / min. After drying, a protective coating is formed on the side of the molecular sieve layer away from the carrier, resulting in an inorganic membrane.

[0087] 4) Utilize Figure 2 The process involves using an inorganic membrane to perform a separation selectivity test on a gas mixture containing equimolar amounts of helium and methane. The feed flow rate of the mixed gas was controlled at 100 mL / min. −1 15 mL·min -1 Argon gas is used to purge the permeation side, and the feed pressure is controlled at 0.3 MPa by a back pressure valve.

[0088] Example 2

[0089] The method of helium extraction in Example 2 is basically the same as that in Example 1, except that the mass ratio of PDMS, curing agent and n-heptane in the PDMS impregnation solution is 1:0.1:10 and the concentration of PDMS is 9.1%.

[0090] Example 3

[0091] The method of helium extraction in Example 3 is basically the same as that in Example 1, except that the mass ratio of PDMS, curing agent and n-heptane in the PDMS impregnation solution is 1:0.1:15 and the concentration of PDMS is 6.2%.

[0092] Example 4

[0093] The method of helium extraction in Example 4 is basically the same as that in Example 1, except that the temperature of the second drying treatment is 25°C.

[0094] Example 5

[0095] The helium extraction method in Example 5 is basically the same as that in Example 1, except that the impregnation solution is a 1% β-cyclodextrin impregnation solution. The preparation method is as follows: weigh 1g of β-cyclodextrin powder and pour it into 100g of deionized water, then stir. To ensure complete dissolution of the β-cyclodextrin, the process is carried out in a water bath at 50-60℃, stirring until the solution is clear and transparent. The first impregnation and lifting time is changed to 3s, and the first impregnation and lifting rate is changed to 3cm / s.

[0096] Example 6

[0097] The method of helium extraction in Example 6 is basically the same as that in Example 1, except that an inorganic membrane is used to extract helium from lean helium natural gas. The helium content in the lean helium natural gas is 0.075%, and the test pressure is 1 MPa.

[0098] Example 7

[0099] The helium extraction method in Example 7 is basically the same as that in Example 1, except that the impregnation solution is a 2% β-cyclodextrin impregnation solution, and the mass ratio of β-cyclodextrin to deionized water in the impregnation solution is 2:100. The second impregnation and lifting time is changed to 3 seconds, and the second impregnation and lifting rate is 3 cm / s.

[0100] Example 8

[0101] The method of helium extraction in Example 8 is basically the same as that in Example 1, except that the impregnation solution is a 3% β-cyclodextrin impregnation solution, and the mass ratio of β-cyclodextrin to deionized water in the impregnation solution is 3:100.

[0102] Example 9

[0103] The method of helium extraction in Example 9 is basically the same as that in Example 1, except that the temperature of the second drying treatment is 50°C.

[0104] Example 10

[0105] The method of helium extraction in Example 10 is basically the same as that in Example 1, except that the temperature of the second drying treatment is 150°C.

[0106] Example 11

[0107] The method of helium extraction in Example 11 is basically the same as that in Example 1, except that the temperature of the second drying treatment is 200°C.

[0108] Example 12

[0109] The method of helium extraction in Example 12 is basically the same as that in Example 1, except that in step 2), the STT molecular sieve membrane is prepared: based on Example 1 in invention application CN115414793A, a tubular support is used with a support thickness of 1.5 mm.

[0110] Example 13

[0111] The method of helium extraction in Example 13 is basically the same as that in Example 1, except that in step 2), the STT molecular sieve membrane is prepared by changing the number of synthesis days in the preparation process of the STT molecular sieve layer to 7 days, based on Example 1 in invention application CN115414793A.

[0112] Example 14

[0113] The method of helium extraction in Example 14 is basically the same as that in Example 1, except that the temperature of the first drying treatment is 15°C and the time of the first drying treatment is 4 hours.

[0114] Example 15

[0115] The method of helium extraction in Example 15 is basically the same as that in Example 1, except that the second drying process takes 0.5 hours.

[0116] Comparative Example 1

[0117] The method of helium extraction in Comparative Example 1 is basically the same as that in Example 1, except that the STT molecular sieve membrane (i.e., the surface of the molecular sieve layer facing away from the support is not provided with a protective coating) is directly used to perform separation selectivity tests on a mixed gas containing equimolar helium and methane.

[0118] Comparative Example 2

[0119] The helium extraction methods in Comparative Example 2 and Example 6 are basically the same, except that STT molecular sieve membranes are used to extract helium from lean helium natural gas. The helium content in the lean helium natural gas is 0.075%, and the test pressure is 1 MPa. The results are shown in Table 2.

[0120] Comparative Example 3

[0121] The method of helium extraction in Comparative Example 3 is basically the same as that in Example 1, except that a ceramic support with an effective pore size of 300 nm is used directly to perform separation selectivity tests on a mixed gas containing equimolar helium and methane.

[0122] Comparative Example 4

[0123] The method of helium extraction in Comparative Example 4 is basically the same as that in Example 1, except that the STT molecular sieve membrane is replaced with a ceramic membrane with an effective pore size of 300 nm and coated with a PDMS protective layer.

[0124] Test case

[0125] The high-pressure natural gas helium extraction method involves controlling the flow rate Q of the feed gas through a mass flow controller, and controlling the pressure (p) between 0.1 MPa and 5.2 MPa by a back pressure valve. The feed side of the helium-containing natural gas is under high pressure, while the permeation side is kept at atmospheric pressure or vacuum.

[0126] The permeability (P) of component i i ) and the selectivity of component i to component j (α) i / j The definition is as follows:

[0127]

[0128] Helium recovery rate (R) He Concentration factor (β) He The calculation formulas are as follows:

[0129]

[0130] In the formula, Q is the feed flow rate, Q perm The osmotic flow rate is expressed in mol·s⁻¹. -1 J i The osmotic flux is expressed in mol·m⁻¹. -2 ·s -1 ;Δp i x is the partial pressure difference of component i across the membrane, in Pa; i (x j ) and y i (y j () represents the mole fraction of component i(j) on the feed side and the permeate side, respectively, in %; the membrane area is S, m. 2 .

[0131] Figure 3 (a) is a SEM image of the STT molecular sieve membrane of Comparative Example 1 of the present invention.

[0132] Figure 3 (b) is another SEM image of the STT molecular sieve membrane of Comparative Example 1 of the present invention.

[0133] from Figure 3 (a) is a SEM image of the surface of the STT molecular sieve membrane of Comparative Example 1 of the present invention. Figure 3 (b) is a SEM image of the cross-section of the STT molecular sieve membrane of Comparative Example 1 of the present invention. Figure 3 In (b), the dashed line represents the boundary between the membrane layer and the support, and 4.8 ± 0.8 μm represents the thickness of the STT molecular sieve membrane layer. From Figure 3 (b) It can be seen that the surface of the STT molecular sieve membrane in Comparative Example 1 is not protected by a coating.

[0134] Figure 4 (a) is a SEM image of an inorganic membrane for helium extraction according to Embodiment 2 of the present invention.

[0135] Figure 4 (b) is another SEM image of the inorganic membrane for helium extraction in Embodiment 2 of the present invention.

[0136] from Figure 4 (a) is a SEM image of the surface location of the inorganic membrane used for helium extraction in Embodiment 2 of the present invention. Figure 4 (b) is a SEM image of the cross-sectional position of the inorganic membrane used for helium extraction in Embodiment 2 of the present invention. Figure 4 In (b), 2 μm represents the thickness of the protective coating, and the dashed line on the left indicates the boundary between the molecular sieve layer and the support. From Figure 4 (a) and Figure 4 (b) It can be seen that the inorganic membrane surface of Example 2 is completely covered by the PDMS protective coating, and no crystal particles are visible. Moreover, the PDMS protective coating is uniformly applied to the surface of the STT molecular sieve membrane.

[0137] Figure 5 (a) is a schematic diagram of the contact angle of the STT molecular sieve membrane of Comparative Example 1 of the present invention.

[0138] from Figure 5 (a) It can be seen that the contact angle of the STT molecular sieve membrane in Comparative Example 1 is 61°, which shows hydrophilicity.

[0139] Figure 5 (b) is a schematic diagram of the contact angle of the inorganic membrane for helium extraction in Embodiment 1 of the present invention.

[0140] from Figure 5 (b) It can be seen that the inorganic membrane used for helium extraction in Example 1 has a contact angle of 121°, exhibiting excellent hydrophobicity.

[0141] Figure 6 This is a stability diagram of the inorganic membrane used for helium extraction in Embodiment 1 of the present invention for separating helium from a mixed gas containing helium and methane.

[0142] from Figure 6 It can be seen that after being stored in air for a certain period of time, the inorganic membrane of Example 1 still maintains good selectivity for separating helium in a mixture of helium and methane.

[0143] Table 1

[0144] Group Thickness of protective coating / μm Carrier thickness / mm Molecular sieve layer thickness / μm <![CDATA[α He / CH4 ]]> Example 1 2 0.5 4 53.6 Example 2 2.4 0.5 8 86.8 Example 3 1.7 0.5 10 49.5 Example 4 2.7 0.5 8 181 Example 5 0.5 0.5 4 36 Example 6 2.5 0.5 4 34 Example 7 0.7 0.5 8 24 Example 8 1 0.5 7 24.6 Example 9 2.5 0.5 6 65 Example 10 1.5 0.5 8 44.4 Example 11 1.2 0.5 4 44 Example 12 2.6 1.5 6 50 Example 13 2.5 0.5 15 41 Example 14 2.7 0.5 6 53 Example 15 2.4 0.5 4 54 Comparative Example 1 - 0.5 6 20 Comparative Example 2 - 0.5 7 13.2 Comparative Example 3 - 0.5 - 1.2 Comparative Example 4 - 0.5 - 1.5

[0145] As shown in Table 1, compared with the comparative example, the inorganic membrane for helium extraction provided by the present invention includes a molecular sieve membrane and a protective coating. The protective coating includes β-cyclodextrin and / or polydimethylsiloxane. The presence of the protective coating enables the inorganic membrane to have high selectivity for separating helium in a mixed gas containing helium and methane, and the hydrophobicity of the protective coating can extend the service life of the inorganic membrane, making the storage and application process of the inorganic membrane simpler.

[0146] As can be seen from the comparison between Example 1 and Comparative Examples 1-4, the inorganic membrane for helium extraction provided by the present invention can improve the separation selectivity of helium relative to methane.

[0147] It should be noted that the STT molecular sieve membrane in Comparative Example 1 needs to be placed at 473K for 12 hours before testing to remove moisture or other adsorbed components from the molecular sieve pores. The inorganic membrane in Example 1, however, does not require heat treatment and can be tested directly.

[0148] The ceramic support in Comparative Example 3 lacks the ability to separate helium from a mixture of helium and methane, with a separation selectivity of only 1.2. The results of Comparative Example 4 indicate that the PDMS protective layer itself does not possess the ability to separate helium from a mixture of helium and methane. Therefore, it can be concluded that the improved separation selectivity of the STT molecular sieve membrane with the PDMS protective layer for helium in a mixture of helium and methane mainly originates from the elimination of intergranular defects.

[0149] Table 2

[0150] <![CDATA[p feed a ]]> <![CDATA[P He b ]]> <![CDATA[F He c ]]> β <![CDATA[α He / CH4 ]]> <![CDATA[R He / %]]> 0.1 43.0 0.30 28.3 40.4 1.0 1.1 24.6 1.94 12.0 13.2 6.8 2.1 18.8 2.89 8.3 8.7 10.1 3.1 17.7 4.09 6.7 6.0 14.4 4.1 16.7 5.06 5.8 6.0 17.7 5.1 15.6 5.85 5.3 5.4 20.2

[0151] a MPa; b :×10 -10 mol·m -2 ·s -1 Pa -1 ; c :×10 -6 mol·m -2 ·s -1 ;F He : Permeation helium flux.

[0152] Figure 7 This is a graph showing the helium separation performance of the inorganic membrane used for helium extraction in Embodiment 6 of the present invention for a mixed gas containing helium and methane.

[0153] From Table 2 and Figure 7 It can be seen that, within a certain range, the selectivity of helium for separating methane decreases significantly with increasing pressure. Figure 7 α in He / CH4 α is obtained by calculation using Equation 2. i / j In this context, i represents He, j represents CH4, and β represents...He R is obtained by calculation using Equation 4. He Calculations using Equation 3 show that, at 5.1 MPa, the helium selectivity for methane separation in Example 6 remains as high as 166 (i.e., ...). Figure 7 α in He / CH4 The helium concentration factor can reach up to 92, and the helium concentration can be increased from 0.075% to 6.9% after a single-stage membrane separation. Table 2 shows that in Comparative Example 2, for a natural gas feed with a helium content of 0.075%, calculations using Equation 4 show that the He concentration on the permeate side of the STT molecular sieve membrane can be increased to 2.10% at 0.1 MPa, with a concentration factor of 28.3. However, as the feed pressure increases, the helium concentration factor gradually decreases to around 5, possibly due to the presence of numerous intergranular defects in the STT molecular sieve membrane.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An inorganic membrane for helium extraction, characterized in that, Including molecular sieve membranes and protective coatings; The molecular sieve membrane includes a carrier and a molecular sieve layer, and the protective coating is located on the surface of the molecular sieve layer opposite to the carrier. The protective coating includes β-cyclodextrin and / or polydimethylsiloxane.

2. The inorganic membrane according to claim 1, characterized in that, The molecular sieve layer includes STT molecular sieve.

3. The inorganic membrane according to claim 1 or 2, characterized in that, The thickness of the protective coating is 0.5-3 μm.

4. The inorganic membrane according to any one of claims 1-3, characterized in that, The thickness of the carrier is 0.5-1.5 mm; And / or, the thickness of the molecular sieve layer is 4-15 μm.

5. A method for preparing an inorganic membrane according to any one of claims 1-4, characterized in that, Includes the following steps: 1) The molecular sieve membrane is placed in the impregnation solution and subjected to a first impregnation and lifting treatment and a second impregnation and lifting treatment in sequence to obtain an impregnated molecular sieve membrane; the impregnation solution includes functional components, the functional components including β-cyclodextrin and / or polydimethylsiloxane; 2) The impregnated molecular sieve membrane is subjected to a first drying treatment and a second drying treatment in sequence to obtain the inorganic membrane.

6. The method for preparing the inorganic membrane according to claim 5, characterized in that, The first immersion lifting treatment time is 3-40 seconds, and the first immersion lifting treatment rate is 0.2-3 cm / s; And / or, the second immersion lifting treatment time is 3-40s, and the second immersion lifting treatment rate is 0.2-3cm / s; And / or, the temperature of the first drying treatment is 15-30°C, and the time of the first drying treatment is 1-4 hours; And / or, the temperature of the second drying treatment is 25-200℃, and the time of the second drying treatment is 0.5-1h.

7. The method for preparing the inorganic membrane according to claim 5 or 6, characterized in that, The functional component includes polydimethylsiloxane, and the concentration of polydimethylsiloxane is 6-20%. The functional component includes β-cyclodextrin, and the concentration of β-cyclodextrin is 1-3%.

8. The method for preparing the inorganic membrane according to any one of claims 5-7, characterized in that, The functional component includes polydimethylsiloxane, and the impregnation liquid also includes a curing agent and n-heptane; The mass ratio of polydimethylsiloxane, curing agent, and n-heptane is 1:0.1:(5-15); The functional component includes β-cyclodextrin, and the impregnation solution further includes deionized water; the mass ratio of β-cyclodextrin to deionized water is (1-3):

100.

9. A method for extracting helium, characterized in that, Includes the following steps: The inorganic membrane is used to adsorb helium from a mixed gas containing helium and methane, wherein the inorganic membrane includes the inorganic membrane according to any one of claims 1-4 or the inorganic membrane prepared by the method of preparing the inorganic membrane according to any one of claims 5-8.

10. The helium extraction method according to claim 9, characterized in that, The adsorption pressure is 0.1-5.2 MPa.

Images